Continuously variable transmission device

ABSTRACT

A continuously variable transmission device of the type having planetary members ( 25 ) in rolling contact with radially inner ( 23 ) and outer ( 26 ) races each comprising two axially spaced parts, with control means ( 30 ) for selectively varying the axial separation of the two parts of one race and thus the radial position of the planetary members ( 25 ) in rolling contact therewith, in which there are provided means sensitive to the torque applied to a drive-transmitting member of the transmission operable both to determine the compensating variation in the separation of the two parts of the other race and thus the transmission ratio of the device and to vary the forces exchanged between the planets ( 25 ) and the races ( 23, 26 ) normal to the interface between them.

The present invention relates generally to a continuously variabletransmission device, and particularly to such a device in which forcesare transmitted by rolling traction.

One known type of continuously variable transmission, which has been putinto commercial use in the drive train of a motor vehicle comprises atransmission belt of trapezoidal section passing around two splitpulleys the opposite halves of which have facing inclined conicalsurfaces and are urged towards one another such that the effectivetransmission ratio between one pulley and the next is determined by therelative separation of the two parts of the pulleys. On being movedapart, the two parts of a pulley allow the belt to contact the conicalfaces at a radially inner position thereby changing the transmissionratio.

In this case the resilient forces exerted on the two parts of the otherpulley cause them to move together to compensate for the reduction intension in the belt thereby increasing the radius of the contact betweenthe belt and the pulleys. Such transmission devices are, however,relatively large as they comprise two substantially spaced shafts, andmoreover are not capable of rapid ratio change. They also tend to havelow efficiency under part load operation. Versions having rubber beltscan also be subject to large amounts of wear largely because of thesliding friction which takes place between the belt and the pulleys asthe gear “ratios” are changed. It does have the advantage overconventional gear boxes of providing a continuous or stepless variationin drive transmission from a minimum to a maximum drive ratio. It isnot, however, capable of providing a reverse ratio without furtherstructural complications.

Other forms of continuously variable transmission are known, for examplefrom U.S. Pat. No. 1,800,388. The present invention seeks to provide acontinuously variable transmission in which the forces are transmittedbetween the members in motion by rolling contact. This minimises theamount of wear to which the members are subject upon changing thetransmission ratio, and allows a continuously variable transmission tobe made which is easy to control, requires low maintenance and offers adurable mechanism with a long service life.

According to one aspect of the present invention, therefore, there isprovided a continuously variable transmission device of the type havingplanet members in rolling contact with radially inner and outer raceseach comprising two axially spaced parts, with control means forselectively varing the axial separation of the two parts of one race andthus the radial position of the planet members in rolling contacttherewith, in which there are provided means sensitive to the torqueapplied to a drive-transmitting member of the transmission operable bothto determine the compensating variation in the separation of the twoparts of the other race and thus the transmission ratio of the deviceand to vary the forces exchanged between the planets and the racesnormal to the interface between them.

In a preferred embodiment of the invention the planet members aresubstantially spherical bodies. They may be right circular, oblate orprolate spheroids. Alternatively, the planet members may have respectivefirst and second surface portions comprising surfaces of revolutionabout the same axis (for each member) the surface portions beinginclined with respect to one another in opposite directions about theaxes of revolution. The planet members may have a convex or concavesurface of revolution defined by a curved generatrix which may be aregular or irregular curve or a part-circular curve. In the case of apart-circular generatrix this may be a semi-circle, in which case thesurface of revolution of the planet member is spherical.

In such a structure the inner and outer races preferably comprises twoparts, one in contact with each of the first and second portionsrespectively, and each having a respective surface constituted by asurface of revolution about a common axis and inclined in oppositedirections with respect to the said axis. The two parts of one of theinner or outer races may be supported in such a way as to be relativelydisplaceable towards or away from one another whereby to vary the radiusof the point or line of contact between the said one race and the planetmembers.

Embodiments of the invention may be provided with torque-sensitivemechanical coupling means interposed between an input drive member andone of the races whereby to balance the torque transmission and thecontact pressures between the two parts of that race and the planetmembers.

In practice, it is preferred that the planet members are substantiallyspherical and captive between the radially inner races and the radiallyouter races, there being roller follower members circumferentiallyintercalated between adjacent pairs of planet members for transmittingdrive to or from the said planet members. In such an arrangement it isparticularly convenient if the roller follower members are carried on aplanet carrier member to which drive to or from the planet members istransmitted in operation of the device.

In general terms, the present invention provides a drive transmissiondevice as defined above, in which the axes of rotation of the planetmembers about their own axis are substantially parallel to the axis ofrotation of the planets about the radially inner race. In such a drivetransmission device it is a particular feature that the axis of rotationof the radially inner race is substantially parallel to the axis of themeans defining the radially outer race defining the planetary path ofthe planet members.

In any event it is convenient if the means for selectively varying theaxial separation of the two parts of the radially inner race or themeans defining the radially outer race include two adjustment membersinterconnected by a helical interengagement such that relative turningmotion of one of the adjustment members results in relative axialdisplacement of the other. In such a device the helical interengagementof the two adjustment members comprises a screw threaded engagement ofthe members themselves, the said one of the two adjustment members beingturnable through at least a limited arc of movement about a first axisand the said other of the adjustment members being restrained againstrotary motion at least about an axis substantially parallel to the saidfirst axis. The helix angle may be constant over the entire length ofthe helix although for certain applications it may be found to be usefulif the helix angle of the said helical interengagement varies over thecircumferential extent of the helix.

In general, it is convenient if the said other of the two adjustmentmembers is or is carried by or on the said means defining the radiallyouter track. The two parts of the radially inner race may be carried ona drive or driven shaft, and the means for allowing relative separationof the two parts of the radially inner race comprise at least oneinclined surface acting to react the forces exerted by the transmissionof drive forces between the radially inner race and the planet members.The said inclined surface may be part of a helical interengagementbetween the parts of the radially inner race and the drive shaft. Thehelix angle may be constant or may vary over the length of the helix.

Whether the helix is constant or varying its form and helix angle shouldpreferably be such that the circumferential component of the axial forcereacted by the helix is substantially equal to and opposite in sign fromthe direct circumferential force reacted by the helix such that theforce required to be applied to the said selective adjustment means tomaintain or change a transmission ratio is minimised.

The present invention also comprehends an infinitely variabletransmission device comprising a continuously variable transmission asdefined above together with a further epicyclic transmission train offixed ratio gears or rolling traction members the dimensions of whichare such that the effective radius of contact between the gears aboutthe axes of the input shaft lies at a radius between the maximum andminimum radius of the line of contact between the radially inner raceand the planets at opposite ends of the range of adjustment of thecontinuously variable transmission.

In such an embodiment when the radius of the line of contact between theplanet members and the radially inner race of the continuously variabletransmission is equal to the contact radius between the radially innerrace and the planets of the epicyclic drive train of fixed ratio gearsthere is no effective transmission of torque and the torque transmissionis delivered in one rotary direction or the other depending on whetherthe adjustment of the continuously variable transmission moves the lineof contact between the planet members and the radially inner race to apoint greater than or less than the radius of contact of the fixed ratioepicyclic gear train. This makes it possible to provide both forward andreverse transmission ratios.

In another aspect the present invention provides a rolling contactcontinuously variable transmission device of the type having planetarymembers in rolling contact with radially inner and outer races eachcomprising two relatively axially displaceable race parts, in which theplanetary members are substantially spherical and the transmissionforces to or from the spherical planetary members in planetary motion iseffected via roller follower members.

In a practical embodiment the roller follower members are eachinterposed between respective pairs of adjacent planetary members andcarried on a planet carrier member through which drive to or from theplanet members is transmitted in operation of the device.

The rolling contact continuously variable transmission device of theinvention may be considered, in one aspect, as a variable geometry fourpoint contact rolling element bearing in which power transfer takesplace between two or three principal bearing elements comprising aradially inner race, a radially outer race and a planet carrier or cage;a fourth bearing element being provided, usually fixed, for torquereaction.

In a transmission device formed as an embodiment of the invention theaxial separation of the race which compensates for adjustment of theother is therefore determined in essence by the forces applied to thesaid other race elements. Such a continuously variable transmission maybe combined with an epicyclic gear train to provide an infinitelyvariable transmission which has a transmission ratio varying from anegative value or nil to a maximum value determined by the dimensions ofthe device. It is also possible so to chose the relative shapes of thecontacting surfaces of the races and the rolling elements that aso-called “geared” neutral position can be achieved in which notransmission of motion takes place despite the rotation of the drivemember. Such a configuration also, therefore, allows the rollingelements to be in such neutral position at an intermediate point intheir overall range of movement (which movement is determined by thecontrolled separation of that pair of the race members to which inputcontrol forces are applied) thereby allowing relative rotation of theinput and output drive members in the same or in opposite directionsdepending on the adjustment of the transmission. This effectivelyresults in the provision of forward and reverse drive ratios on eitherside of a neutral ratio.

Although such transmissions can be controlled in such a way thatinfinitely variable transmission ratio control can be effected, suchcontrol is unfamiliar to the majority of users in view of the almostuniversal use of stepped or incremental drive transmission ratiosavailable from gearboxes used for effecting such ratio changes.Embodiments of the present invention can be made in which incrementalcontrol of the gear ratios is achieved by various means whereby tosimulate a stepped gearbox. In one embodiment a control mechanism bywhich the separation of the two controlling raceways is determined hasan incremental adjustment device or indexing mechanism allowing it to bedisplaced between several discrete predetermined positions.Alternatively, the contacting surface of some of the raceways may beshaped such that the forces exerted on the rolling elements tend todrive them to one of a limited number of predetermined positions.

Although a “geared” neutral has many advantages in a transmission devicesuch as that defined herein inevitable tolerances may result in theirbeing a certain amount of “creep” in either direction when thetransmission device is set in its neutral position. To combat this itmay be advantageous to provide means by which a “disconnected” neutralratio may be achieved in which there is a positive break in thetransmission chain allowing certainty in the selection of a neutral gearthat no drive transmission will take place.

A disconnected neutral may be achieved in one aspect of the presentinvention by the addition of a relatively rotatable member orcorresponding members, to either the radially inner or radially outerraceway contactable by the rolling elements over a certain part of therange of movement thereof in adjustment of the drive transmission. Whenthe rolling elements are in contact with such relatively rotatablemembers the effective decoupling of the rolling elements from theraceways ensures that drive transmission does not take place in thisadjustment.

A disconnected neutral may also be achieved by mounting one of the partsof the raceway in such a way that it can be withdrawn from its workingposition by a distance such as to release the pressure on the rollingelements at the time. This allows, in effect, a “declutching” action tobe achieved with the transmission device set in any gear ratio.

A similar arrangement may be provided for a so-called “launch” controlthat is for progressive engagement of the transmission device fromneutral to a drive gear ratio, and this can be achieved effectively byproviding a range of motion of a ratio control member between the gearedneutral position and a first detent or stop defining a lowermost gearratio.

In some embodiments of the present invention described so far the drivetransmission from an input shaft to an output shaft can only take placein one direction of rotation. This arises because the torque-sensingmechanism, which in one embodiment involves a helical interengagementbetween one of the two race parts in the said other race and acooperating component allows the two race parts to be urged towards oneanother by the forces exerted on them in operation only when thedirection of rotation of the input shaft corresponds to that of thehelical interengagement. Relative rotation between the input shaft andthe output shaft in the opposite direction would result in a relativeseparation of the other race parts which would effectively result in areduction in the contact forces and, ultimately, to a decoupling of theinput and output members. This, of course, has certain advantages insome circumstances, particularly where an over-run free-wheel effect isdesirable. However, for use as a motor vehicle transmission, especiallyone in which engine over-run is used for braking, the free-wheel effectis unwanted and, indeed, decidedly undesirable.

The present invention also seeks, therefore, to provide a continuouslyvariable transmission device of the type described herein in which thetransmission of torque from an input to an output shaft can take placein either direction of rotation.

According to another aspect of the present invention, therefore, thereis provided a continuously variable transmission device of the typehaving planetary members in rolling contact with radially inner andouter races each comprising two axially spaced parts, with control meansfor selectively varying the axial separation of the two parts of onerace and thus the radial position of the planetary members in rollingcontact therewith, in which there are provided means sensitive to thetorque applied to a drive-transmitting member of the transmissiondevice, operable both to determine the compensating variation in theseparation of the two parts of the other race and thus the transmissionratio of the device and to vary the forces exchanged between the planetsand the races normal to the interface between them, and in which thesaid torque-sensitive means include the two axially spaced, relativelymoveable parts of the said other race, each said part being itselfaxially movable in two directional senses from a central position andengagable by limit stop means whereby to allow the transmission ofrotary drive from a rotary drive input member to a rotary drive outputmember of the transmission device in each of two opposite senses ofrotation.

In a preferred embodiment of the invention the said relatively movablerace parts of the torque-sensitive means are interconnected with theinput drive member by a screw-thread engagement of the same hand bywhich rotary drive is transmitted when axial displacement of a race partis restrained.

The thread flights of the screw thread engagement are preferablyinterengaged by rolling elements such as balls although this is notessential. The provision of interengaging balls helps significantly toreduce frictional resistance in the device.

The said two relatively movable race parts of the torque-sensitive meansmay be oppositely axially resiliently biased. This resilient bias act to“prime” the torque-sensing reaction of the device and in a preferredembodiment of the invention the resilient biasing of the said tworelatively movable race parts is achieved by a compression springlocated between them.

Of course, in order to ensure that bi-directional rotation can takeplace each of the two race parts must ultimately be restrained fromaxial movement such that the other race part can, effectively “screw up”against it by the helical action exerted on it by the input member. Suchlimit stop means may comprise respective abutments on or carried by orassociated with the said input drive member.

In one embodiment of the invention the two race parts of the said onerace of the transmission device, the axial separation of which isselectively variable, are each carried on a casing of the transmissiondevice in such a way as to have a limited rotational displacement ineach of two opposite rotational senses. The relative axial separation ofthe two race parts of the said one race may be achieved by a helicalinterengagement of at least one of the two race parts with a fixedmember of the transmission device, the two race parts both beingrelatively turnable with respect to the said fixed member. Such relativeturning movement of the two race parts of the said one race may beachieved by any means which act directly between them rather thanbetween one member and a fixed part. One means by which this can beachieved comprises a Bowden cable acting between the two race parts.

The present invention also comprehends, independently of the structureallowing bi-directional rotation to be achieved, a continuously variabletransmission device of the type having planetary members in rollingcontact with radially inner and outer races each comprising two axiallyspaced parts, with control means for selectively varying the axialseparation of the two parts of one race and thus the radial position ofthe planetary members in rolling contact therewith, in which theplanetary members each have a circumferential annular groove the axis ofwhich substantially coincides with the respective rolling axis aboutwhich each planetary member turns as it rolls in contact with the races,the said annular grooves being engaged by roller follower members actingto guide the planetary members to maintain their orientation in theirplanetary motion.

This latter feature enables a greater load-carrying capacity to beachieved because a greater number of planetary members can be arrangedin a given annular space because the circumferential space occupied by aplanetary member can overlap that occupied by a planet follower.

The planet followers are preferably carried by a common carrier memberthrough which drive transmission is conveyed to an output drive memberof the device.

According to a further aspect of the present invention a continuouslyvariable transmission device of the type having planetary members inrolling contact with radially inner and outer races each comprising twoaxially spaced parts, with control means for selectively varying theaxial separation of the two parts of one race and thus the radialposition of the planetary members in rolling contact therewith, hasplanetary members each with arcuately curved surface portions in rollingcontact with correspondingly curved portions of the respective races,the radius of curvature of the said surface portions of the planetarymembers being greater than the effective radius of the planetary memberitself.

This can be visualised by imagining the planetary members as spheres ofa given diameter notionally split to remove a central portion andreassembled with the remaining quadrants in contact with one another.The radius of curvature of the surface portions will thus match that ofthe “original” sphere whilst the diameter of the newly-assembled spherewill be less than the diameter of the original sphere. Such planets mayalso be formed with circumferential grooves for receiving rollerfollower guide members as discussed above. There may further be providedmeans for guiding the planetary members to maintain the orientation oftheir rolling axes as they roll over the contacting surfaces of theraces. Such guide members may be the above-mentioned rollers engaged inthe circumferential grooves.

The purpose of enlarging the radius of curvature of the surface portionsin relation to the diameter of the planetary member itself, is to extendthe range of ratios which can be transmitted by the transmission device.In a specific embodiment, which will be described in more detailhereinbelow, the ratio range can be extended to 4.3:1.

In a further aspect of the present invention, which may be consideredindependently of the other aspects described hereinabove, there isprovided a continuously variable transmission device of the type havingplanetary members in rolling contact with radially inner and outer raceseach comprising two axially spaced parts, with control means forselectively varying the axial separation of the two parts of one raceand thus the radial position of the planetary members in rolling contacttherewith, in which each planetary member has a plurality of elementaryannular contact surface portions having a substantially constantinclination to the rolling axis of the planetary member itself.

This allows the continuously variable transmission to be provided withpreferred adjustment positions effectively representing specific gearratios of a conventional gear box. Increased load-bearing capacity isalso achieved by providing what amounts to a line rather than a pointcontact between the planets and the races over the surface portionshaving substantially constant inclinations.

This can be viewed as a planetary member having a generatrix whichincludes a section comprising a plurality of substantially rectilinearelementary portions. The races may have substantially continuouslycurved contact surfaces or may have respective contact surfaces forrolling contact with the planetary members, each having correspondinglyinclined elementary annular contact surface portions substantiallymatching those of the planetary members.

Various embodiments of the present invention will now be moreparticularly described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic axial section of the major component of a rollingcontact continuously variable transmission device useful for explainingthe principle of operation of the device;

FIG. 2 is a schematic axial view of the transmission device seen fromthe direction of the arrow A of FIG. 1;

FIGS. 3 and 4 are schematic axial sections similar to FIG. 1 andrespectively showing the transmission device in this configuration forthe highest transmission ratio and that for the lowest transmissionratio;

FIG. 5 is an axial sectional view of a continuously variable rollingcontact transmission device formed as a first embodiment of the presentinvention;

FIG. 6 is a schematic axial sectional view showing a rolling contactcontinuously variable transmission device incorporated in an infinitelyvariable transmission device;

FIG. 7 is an axial sectional view of a further embodiment of theinvention suitable for use as a bicycle hub gear transmission;

FIGS. 8, 9 and 10 are schematic partial axial sectional views of variousdifferent raceway configurations useful for various specificapplications;

FIGS. 11 and 12 are schematic axial sectional views of alternativeembodiments having different planetary members;

FIG. 13 is an axial sectional view through a first embodiment of thepresent invention;

FIG. 14 is a cross-sectional view taken on the line XIII—XIII of FIG.13;

FIGS. 15 and 16 are schematic detail views showing components of theembodiment of FIGS. 13 and 14 in two different operating configurations;

FIG. 17 is a schematic cross-sectional view of the embodiment of FIG. 13showing the relative positions of an adjustment mechanism;

FIG. 18 is an axial sectional view of an alternative embodiment of theinvention; and

FIGS. 19-24 are schematic views of a detail of the embodiment of FIG. 18showing the components in different configurations for achievingdifferent gear ratios.

Referring first to FIGS. 1 to 4, the continuously variable transmissionmechanism of the invention is formed as a variable radius epicyclicmechanism having rolling traction torque transfer with the advantagethat the shaft bearings and housing are not subject to large forces andthe moving parts can be based on traditional roller and ball bearingtechnology. It also has the advantages that it includes a purelymechanical preload and torque sensing system and that it can be splashor grease lubricated by a known traction fluid lubricant withoutrequiring special lubricating techniques. As will be appreciated fromthe more detailed description which follows, the control of thetransmission ratio can be effected by a simple mechanical device.

The variable radius epicyclical transmission device in FIGS. 1 to 4,sometimes referred to as a variator, comprises a housing (not shown forsimplicity) within which is mounted an input shaft 11 bearing rollingelement bearings 12, 13 within a planet cage 14 carrying three planetfollower members 15. The planet follower members 15 are rotatably borneon the planet cage 14 by planet follower shafts 16.

The planet cage 14 is effectively constituted by two radial plates 14 a,14 b joined together by shouldered studs 16 forming the said planetfollower shafts and secured by nuts 20, 21 at each end to form a cage.An axial cylindrical extension 22 of the radial plate 14 b of the planetcarrier 14 constitutes the output shaft of the transmission mechanism.

On the input shaft 11 is carried a radially inner race 23 constituting asun member comprising two parts 23 a, 23 b which are engaged to theshaft 11 by means of a coupling comprising a helical interengagement inthe form of a screw threaded engagement. The two race parts 23 a and 23b have oppositely handed threads so that, for reasons which will bedescried in more detail below, a relative rotation of the input shaft 11and the inner race parts 23 a, 23 b in one directional sense will causethe two parts to be displaced towards one another whereas axialseparation of the two parts 23 a, 23 b of the inner raceway occurs wherethere is relative rotation between them and the input shaft 11 in theopposite directional sense.

Three spherical planetary members 25 are engaged between the innerraceway 23 and an outer raceway 26 also comprising two axially separatedannular raceway members 26 a, 26 b. Rolling tracks of the racewaymembers 23 a, 23 b and 26 a, 26 b, respectively identified 27 a, 27 band 28 a, 28 b each comprise, in cross-section, a part-circular arcuatesurface the radius of which is slightly greater than the radius of thespherical planetary members 25.

The outer raceway members 26 a, 26 b are engaged by an axial adjustmentmechanism generally indicated 29 and schematically shown in FIG. 1 as alever 30 pivotally mounted on a reaction member 31 such that turning thelever in one direction or the other about a pivot 32 by which it isconnected to the reaction member 31, and as shown by the double arrow Bof FIG. 1, causes the two raceway parts 26 a, 26 b to be urged axiallytowards one another or allowed to separate axially from one another. Theraceway 26 is provided with means for preventing its rotation about theaxis X—X which is the common axis of rotation of the input shaft 11, theinner and outer raceways 23, 26, the output shaft 22 and the sphericalplanetary members 25.

In operation of the transmission rotation of the shaft 11 is transmittedto the inner raceway 23 rotation of which causes rotation of the balls25 by rolling contact therewith, the balls 25 rolling over thestationary raceway 26. Rotation of the balls 25 is transmitted via theroller followers 15 to the roller cage 14 and thus to the output shaft22. By displacing the lever 30 in one direction or the other the twoparts 26 a, 26 b of the outer raceway can be urged towards one anotheror allowed to move axially away from one another. Axial approach of thetwo outer raceway members 26 a, 26 b applies pressure to the planetaryballs 25 causing them to move radially inwardly of the transmissiondevice urging the two inner raceway parts 23 a, 23 b apart. The helicalinterengagement between the radially inner raceway parts 23 a, 23 b andthe input shaft 11 acts in effect as a torque-sensitive mechanism inthat the helical interengagement is such that rotation of the shaft 11in the intended direction of drive causes the raceway parts 23 a, 23 bto approach one another axially when resisted by drag so that any playin the rolling contact between the raceways and the planetary balls 25is taken up and compensated by the tendency of the raceway parts 23 a,23 b to approach one another until the forces exerted on the helicalinterengagement between the raceway parts 23 a, 23 b and the drive shaft11 matches the reaction forces between the raceway parts 23 a, 23 b andthe planetary balls 25, at which point no further relative axialdisplacement of the raceway parts 23 a, 23 b takes place and drivetransmission takes place at a transmission ratio determined by theradial position of the balls 25 when this occurs.

In the configuration illustrated in FIG. 4 it will be seen that theradius of rolling contact between the balls 25 and the inner raceway 23is relatively large and the radius of contact between the balls 25 andthe outer raceway 26 is relatively small. In this configuration thetransmission ratio between the input shaft 11 and output shaft 22 is atits lowest. By allowing the lever 30 to move in the opposite direction,however, the raceway parts 26 a, 26 b are allowed to move apart so thatthe balls 25 can move radially outwardly compensated by axial approachof the inner raceway parts 23 a, 23 b.

The difference between the curvature of the curved surfaces 26 a, 26 b,27 a, 27 b of the raceways 23, 26 and the spherical planet members 25will determine the precise shape of the contact patch which in practiceexists between the members in rolling contact. Although in an idealisedsituation the contact would be a point contact, in practice, because theinterior of such a variable transmission would contain a lubricant inthe form of a special traction fluid which both lubricates the movingparts and enhances the rolling traction between them, the points ofcontact will constitute contact patches which are larger the closer theradii of the contacting surfaces are to one another. It is, of course,undesirable that these patches should be too large in order to avoid theso-called spin loss resulting from forces developing in the hydrodynamicfluid between the two elements in rolling contact.

The continuously variable transmission mechanism described above isextremely compact and highly efficient, and has no need for apressurised hydraulic circuit for either lubrication or control purposesin order to achieve the required function. It can be in modular form andis scalable readily to accommodate both large and small sizeapplications.

It is appreciated that, of course, if the input shaft 11 were consideredas a unitary member there would be no way in which the two parts 23 a,23 b of the inner race could be fitted over the unthreaded ends of theshaft 11. This, however, could be achieved by forming the input shaft 11as composite member with the unthreaded parts assembled to the threadedparts after the sun members 23 a, 23 b has been fitted thereto.Alternatively, however, the shaft 11 may simply be of smaller diameter,at the end portions which are not threaded, to match the radiallyinnermost dimension of the thread flights allowing the sun parts 23 a,23 b to be slid along them upon assembly.

Although as illustrated schematically in FIG. 1 the separation of thetwo race parts 26 a, 26 b is controlled by a simple lever 30 with asuitable counteracting member 31 applying symmetrical forces to the tworace parts 26 a, 26 b to cause them to move together or apart asdetermined by the movement of the lever 30 it will be appreciated thatin a practical embodiment it is necessary to apply the axial forces tothe raceway parts over the entirety of the circumference or at least atseveral symmetrically located positions.

Turning now to FIG. 5 there is shown a practical embodiment in whichthis adjustment is achieved in a way which applies the adjustment forcessymmetrically around the entire periphery of the radially outerraceways. The structure of this embodiment is based on the realisationthat the forces exerted by the spherical planets 25 do not need to betransferred through two planet carrier plates such as 14 a, 14 b of FIG.1 but that they are sufficiently balanced to allow only a single planetcarrier plate to be utilised providing that the input shaft 11 isprovided with suitable bearings in order to prevent axial misalignment.

In this embodiment the same reference numerals are used to identify thesame or similar components as in the embodiment of FIGS. 1 to 4. Theinput or drive shaft 11 carries the variable transmission unit in itsentirety. Such an embodiment is suitable, for example, as the geartransmission from a moped or motor cylce to drive a wheel via a chaindrive. For this purpose the output drive member from the variabletransmission is a chain wheel 33 carried on an external casing 34secured to the periphery of the planet carrier 14 which, in thisembodiment, comprises a single disc having shafts 16 projectingtherefrom. Unlike the embodiment of FIGS. 1 to 4, however, the shafts 16do not pass right through the space between the inner and outer races23, 26.

The drive shaft 11 may, for example, be the output shaft from aninternal combustion engine or other prime mover. It has a projecting endportion 25 of smaller diameter than the main part of the shaft 11carrying one of the two parts (in this case the part 23 a) of the innerraceway 23 secured for rotation with the shaft 11 by a woodruff key 36.In this embodiment, instead of the two radially inner raceway parts 23a, 23 b both being relatively movable with respect to the shaft 11 intheir approach and separation movements, the raceway parts 23 a is fixedfor rotation with the shaft 11 and has an axially extending sleeve 23 cover which the second raceway part 23 b is fitted. The outer cylindricalsurface of the sleeve 23 c and the inner cylindrical surface of thesecond radially inner raceway part 23 b are provided with matchinghelical channels 37, 38 of semicircular cross-section housing aplurality of balls 39. Relative axial separation or approach of the tworaceway parts 23 a, 23 b can be achieved, therefore, by relativerotation of these two parts about the axis of the drive shaft 11. Alight spring 40 engaged between the second of the radially inner racewayparts 23 b and a stationary housing 41 provides a light pre-loading ofthe second radially inner raceway part 23 b to ensure that this alwaysmaintains contact with the spherical planets 25 even in no loadconditions so that the radially inner raceway parts 23 a, 23 b do notbecome axially separated by such a distance that the spherical planets25 become loose and rattle within the track defined by the radiallyinner and outer races 23, 26.

The radially outer race 26 comprises a first part 26 a which has anaxially extending sleeve 42 within which the second of the radiallyouter raceway parts 26 b is fitted. The inner surface of the cylindricalsleeve 42 has a helical ridge 43 of rectangular cross-section and thesecond radially outer raceway part 26 b has on its outer cylindricalsurface a helical channel 44 of corresponding rectangular cross-section.The ridge 43 and channel 44 form a robust scroll similar inconfiguration to an “ajax” screw thread.

The first radially outer raceway part 26 a is rotatably fixed butaxially free on a cylindrical outer wall 45 of the fixed housing 41which carries a projecting lug 47 on which is supported atorque-reaction arm 48 which engages a fixed part of the framework ofthe vehicle to maintain the housing 41 stationary (that is non-rotating)with respect to the vehicle.

The housing 41 also carries a second projecting lug 45 which, in thiscase, is hollow and receives a shaft 50 one end of which projects outfrom the casing 41 and carries a control lever 51 and the other end ofwhich projects into the casing and carries a lever 52 the free end ofwhich is secured to the second radially outer raceway part 26 b.Movement of the control lever 51 about the axis of the pivot pin SOcauses the lever 52 to turn correspondingly and thus cause the racewaypart 26 b to turn about the axis of the device, which is coincident withthe axis of the input drive shaft 11, with respect to the fixed radiallyouter raceway part 26 a. This movement is converted by the helicalinterengagement constituted by the helical channels 44 and helical rib43 into axial approach or separation of the two radially outer racewayparts 26 a, 26 b.

Rotation of the drive shaft 11 thus causes the radially inner race 23 torotate and carry with it, by rolling contact, the planetary spheres 25which roll also over the curved surfaces of the radially outer race 26.As in the generalised embodiment of FIG. 1, the planetary spheres 25 areconstrained only by their contact with the curved surfaces 27 a, 27 band 28 a, 28 b of the radially inner and radially outer races 23, 26respectively but each pair of planetary spheres 25 has a roller followerintercalated circumferentially therebetween so that the planetary motionof the spheres 25 is conveyed to these rollers and, via the shafts 16,to the planet carrier 14 which, in this case, constitutes the entireouter casing of the unit carrying the output sprocket 33 which may, forexample, carry a chain for onward transmission of drive to the wheelthis embodiment includes a further bearing 52 between the rotating outercasing 34 and the fixed inner housing 41. Variation in the relativeapproach or separation of the radially outer raceway parts 26 a, 26 b,caused by turning the control lever 51 in one direction or the other,causes a greater or lesser force to be applied to the planetary balls 25urging them radially inwardly into contact with the radially innerraceway 23. As the two radially outer parts 26 a, 26 b are broughttogether the forces exerted on the planetary balls 25 increases and theradially inner force applied to the radially inner races 23 a, 23 burging these apart is accommodated by relative rotation of the racewaypart 23 b with respect to the raceway part 23 a with the balls 39 in thechannels 37, 38 acting in effect as a torque-sensitive mechanism whichallows compensating rotary movement of the movable inner raceway part 23b with respect to the “fixed” raceway part 23 a, fixed, that is, withreference to the drive shaft 11 against axial movement. The raceway part23 a, rotates at the same speed and with the drive shaft 11 as does theraceway part 23 b apart from a minor variation when relative movementover a limited arc takes place for compensating adjustment of thepressures applied by the planetary spheres 25. High and low ratiotransmission, with a continuous variation between the end points, can beachieved by movement of the lever 51 as described in relation to FIGS. 3and 4.

The function of the inner race thread 37, 38, 39 is to maintain theratio of normal to tangential (tractive) force (n/f) of each planet ballcontact point within a certain range. The ratio must be large enough toensure that excessive slip does not occur (at least 10 for partiallubrication and up to twice that for full hydrodynamic lubrication) butnot so large that a significantly greater normal force is applied thanis needed, which would reduce efficiency, torque capacity and life ofthe unit. It may be mentioned here that a spherical planet shape isunique in behaving perfectly in this role for, when such a planet is inequilibrium under the action of four peripheral contact radial‘squeezing’ forces in the plane of the drawing (the n direction) and adriving force through its centre normal to the plane of the drawing (thef direction), as here, n/f has the same value wherever on the peripherythe contact points may be. This means that the inner and outer race n/fvalues are equal for any ratio setting of the transmission.

A light torsion spring 40 acting between the two inner race halvesprovides sufficient preload to ensure that there is always enoughcontact pressure for the torque sensing mechanism to start working whentorque increases from zero.

The outer race thread 43, 44 must have a pitch coarse enough to effectratio changing between extremes without requiring excessive travel ofthe ratio change lever 51, while not being so coarse that the contactconditions simply force the races apart. The type of transmission shownin FIG. 7 is particularly suited to applications having high torque, lowspeed inputs, such as occur in a bicycle. This is because, with input atthe planet carrier, input torque is reacted at a larger radius and bytwice as many contact patches as when input is at the inner race. Insome case, such as the bicycle, output gearing is required to reduceoutput speed to that required for the application.

The embodiment of FIG. 6 comprises an infinitely variable transmissionhaving both forward and reverse transmission ratios. It comprises acontinuously variable transmission mechanism similar to that describedin relation to FIG. 5 the input side of which is provided with anepicyclic gear train of fixed ratio gears. Again, those components whichare the same as or fulfil the same function as corresponding componentsin the embodiment of FIG. 6 will be identified with the same referencenumerals.

The mechanism for varying the transmission ratio between the input driveshaft 11 and output sprocket 33 is substantially the same as thatdescribed in relation to FIG. 5 and, therefore, only the differencesbetween the embodiment of FIG. 6 and the embodiment of FIG. 7 will bedescribed in detail. The input shaft 11 has an additional fixed ratiosun wheel gear 55 which meshes with a set of planet gears 56 equal innumber to the planet follower rollers 15 and carried respectively on thesame shafts as 16.

The planetary gears 56 mesh with an outer ring gear 57 fixed to an outercasing 59 which carries the output sprocket 33. In this embodiment,because the planetary gears 56 are constantly in mesh with the sun wheel55, rotation of the shaft 11 will cause the planet follower rollers 15to rotate at a given speed when the ring gear 57 and consequently theouter casing 59 (and therefore the output drive sprocket 33) isstationary. The stationary or “neutral” drive condition, therefore,occurs when the radial position of the planetary spheres 25 is such thatthe speed of rotation is the same as that of the roller followers. Thisprovides a “geared” neutral position. Adjustment of the lever 51 tocause the planetary spheres 25 to adopt a radially inner position withrespect to the “neutral” position just described will cause the balls toapply a force to the roller followers 15 such as to slow their speed ofrotation with respect to that at which they would rotate with the ringgear 57 stationary, thus causing transmission of drive torque to thering gear 57 in a first direction. This transmission of drive torque maybe considered as a “reverse” direction and the speed thereof increaseswith a decrease in the radial position of the planetary spheres 25.

By contrast, if the adjustment of the lever 51 is such as to allow anincrease in the radial position of the planetary spheres 25 this willincrease the speed of the spheres causing them to apply a force to theroller followers which will cause the planetary gears 56 meshingtherewith to transmit a force in the “forward” direction to the ringgear 57 which is transmitted via the casing 59 to the drive sprocket 33.Again, further adjustment of the lever 51 causing a further increase inthe radial distance of the planetary spheres 25 from the axis of theinput shaft 11 will increase the gear ratio and consequently the speedof the sprocket 33 for a given input speed of the drive shaft 11.

The embodiment of FIG. 7 is somewhat similar, but instead of having anepicyclic fixed gear train at the input to the continuously variabletransmission device it has such a gear train at the output from thecontinuously variable transmission device. Moreover, the embodiment ofFIG. 7 is adapted particularly for use as a bicycle gear hubtransmission device for which purpose the central shaft is not a driveshaft, but a stationary spindle about which the entirety of the devicerotates. Again, those components which are the same as or fulfil thesame functions as corresponding components in the embodiments of FIGS. 5and 6 will be identified with the same reference numerals.

In this embodiment the central shaft 61 is a stationary fixed shaftwhich has threaded end portions 72, 73 engaged by respective nuts 67, 68which can be screwed on to the threaded end portions 72, 73 to engage aframe portion of the bicycle between respective pairs of washers 69, 74and 75.

The shaft 61 has an axial enlargement 76 adjacent its right hand endfrom which extends a radial flange 77 carrying the fixed casing 41 whichat its left hand end carries the outer ring 57 of an epicyclic fixedratio gear train having a plurality of planetary gears 56 meshing thewith ring gear 57 and a sun gear 55 which is carried by axial mounts 78on the radially inner raceway part 23 a.

The planet carrier 14 of the continuously variable transmission has acylindrical inner sleeve 79 which at its left hand end carries a shapedtubular input member 11 which carries a drive sprocket 62 and is itselfborne by bearings 66 on the stationary shaft 61 and carries an outercasing 64 via bearings 63, 71. The outer casing 64 is the “hub” portionof a bicycle wheel having a radial flange 80 from which the bicyclewheel spokes may project radially.

In operation, rotation of the input sprocket 62, for example by means ofa chain drive conventional for bicycles, causes rotation of the planetcarrier 14 and thus the planetary spheres 25 urged by the rollerfollowers 15 carried by the planet carrier 14. The stationary, radiallyouter race 26 a, 26 b carried on the stationary housing 41 fulfils thesame function as before, and has an adjustment scroll defined by ribsand channels 43, 44 as in the embodiment of FIGS. 5 and 6, and likewisea lever 52 for controlling the circumferential position of the outerraceway part 26 b and thus its axial position relative to the otherouter raceway part 26 a.

The rotation of the planetary spheres 25 is transmitted to the radiallyinner races 23 a, 23 b which, carrying the sun gear 55 of the fixedratio epicyclic gear mechanism causes the planet gears 56 to rotatewhich, because they mesh with the stationary ring gear 57, causes theouter housing 64 to turn with a drive transmission ratio and directionof drive dependent on the adjustment of the radial position of theplanetary spheres 25.

The freewheel function normally provided in a cycle transmission may beincluded within the function of the variator. So long as the preloadbetween the inner race halves is small, that is spring 40 is weak, inthe absence of input torque, as when freewheeling, the planet balls arein only light contact with the races and the amount of drag torquethereby generated is negligible.

In many applications input gearing may be used to increase variatorpower capacity. Since the power capacity of a variator is normallylimited by its torque capacity, while its speed capability is normallymuch greater than required, input gearing may be used to reduce theformer and increase the latter. For example, an electric motor primemover with an output speed of 3000 rpm could be advantageously combinedwith variator input gearing of ratio 3:1, thereby generating a stilltolerable 9000 rpm variator input speed but tripling the power capacityof the variator. In many applications, such additional input gearingwould permit the use of a smaller variator unit.

Referring now to FIGS. 8 to 10 there are shown various alternativeconfigurations for the radially inner and outer races 23, 26. In thedescription of these drawings it will be understood that the part of thedrive mechanism illustrated is only that part relating to the immediatecontact of one rolling element with the radially inner race and theradially outer race. The planetary spheres (which are not shown in thedrawings) are substantially identical to those in the embodiments of 5to 7.

In the embodiment illustrated in FIG. 8, the radially outer race 201 hasa curved inner or contact surface 202 having four local annular featuresin the form of sectors of shorter radius of curvature than the overallradius of curvature of the raceway. These annular indentations areidentified with the reference numeral 203 in FIG. 8. It will readily beappreciated that a ball trapped between the outer raceway 201 and innerraceway 204, each of which is split into two parts 201 a, 201 b and 204a and 204 b will settle in contact with one of the four local annularfeatures 203 for preference as a result of the relative inclination ofthe normal to the points of contact between the raceways 201 a, 201 band the planetary ball itself unless this is centred on one of the localannular features 203. This effectively provides for incrementaladjustments which the system will automatically favour so that althoughthe adjustment is infinitely variable it can simulate an incrementaladjustment pattern of a conventional gear box. This also has thebeneficial effect that the stability of the drive transmission in aselected ratio is increased and it lowers the contact stresses. It willof course be appreciated that the annular features 203 illustrated inthe drawing are greatly exaggerated for clarity and that in reality theradius of curvature of each of the annular track parts 203 would have acurvature somewhere between that of the planet ball and that of therace.

FIG. 9 illustrates an embodiment in which a “disconnected” neutralposition is made available. In this embodiment the radially innerraceway 204 is provided with two free rotation rings 205, 206 onemounted in the ring half 204 a and the other in the ring half 204 b.Each of these rings 205, 206 is mounted via, in this case, a ring ofballs 207, 208 respectively such that when the relative separation ofthe two inner race parts 204 a, 204 b is such that the contact betweenthe planet balls (not shown) and the inner races 204 a, 204 b coincidewith the rings 205, 206 the transmission of drive is interrupted by therolling contact of the balls 207, 208.

Turning now to FIG. 10, the alternative embodiment shown comprises asimilar pair of raceways 201, 204 as in the previous two embodiments,but in this case one half 204 b of the inner raceway 204 is axiallydisplaceable in the direction of the arrow A of FIG. 10 by axialdisplacement of a control member 210 engaged with an arm 211 of theinner raceway half 204 b via a bearing 212. Thus, whatever gear ratio isoperative at the time, the drive mechanism can be placed in a “neutral”gear by displacement of the raceway part 204 b.

In any of the embodiments described hereinabove a separate “launch”device may also be provided to control an initial range of movement ofthe controlling races from a “neutral” position to a low “gear” ratio.Such mechanism may provide for a fixed relative displacement of thecontrol races so that the “launch” control mechanism can be utilisedeffectively as a “down shift” whilst the mechanism is in a drivetransmission gear. This will have the effect of lowering the gear ratioby a predetermined amount corresponding to the variation from neutral tothe low gear when used in its “launch” mode.

Turning now to the embodiments of FIGS. 11 and 12 these illustratecontinuously variable drive transmission devices which operate on thesame general principles as those embodiments described above, but inwhich the form of the planets is substantially different, withconsequent variation in other components. Nevertheless, those componentswhich are the same as, or fulfil the same functions as, correspondingcomponents in previously-described embodiments, will be identified withthe same reference numerals. In the embodiment of FIG. 11 the sunmembers 23 a, 23 b together define a radially outer barrel shapesurface, with the sun member 23 a having a curved surface 26 acomprising a surface of revolution generated by an arcuate generatrixinclined in a first direction with respect to the axis of the inputshaft 11 (namely converging towards this axis to the left) whilst thesun member 23 b has an external surface of revolution 26 b constitutedby a surface of revolution generated by a generatrix in the form of anarcuate line diverging from the axis of the shaft 11 towards the left.The curved radially outer surfaces 26 a 26 b of the sun member are inrolling contact with the curved surface 27 of each planet 15 which, inthis embodiment, has what may be described as a “diabolo” shaperepresenting the surface of revolution of a curved line which is convextowards the axis of revolution.

Extending circumferentially around the path followed by the planets 15and in rolling contact therewith, is a track member 28 constituted bytwo separate track parts 28 a, 28 b each having radially inner curvedsurfaces 29 a, 29 b respectively which constitute surfaces of revolutionof arcs which are (but do not have to be) the mirror image of the arcsconstituting the generatrices of the respective axially coincident sunpart 23 a or 23 b. Moreover, the radius of curvature of the arcsdefining the curved surfaces 26 a, 29 a are slightly smaller than theradius of curvature of the curved arcs 27 defining the curved surface ofthe planet 15.

The track member 28 has a dog tooth engaged by a fixed member 31ensuring that the track 28 remains stationary with respect to the casing(not shown). This dog tooth is illustrated purely schematically in FIG.11 it being understood, in practice, the means by which the track 28 isheld stationary within the casing (not shown) may be of different form.

Between the two track members 28 a, 28 b is a cam 32 pivotally mountedabout a point 33 and controlled by a lever 34. Again, only one lever 34is shown in FIG. 11 although, in practice, a mechanism providing forcesacting symmetrically around the circumference of the track 28 will berequired.

Turning now to the embodiment of FIG. 12, this has substantially thesame principle of operation, but differs from the embodiment of FIG. 11in that the planets 15 are formed as two cones 15 a, 15 b joined attheir larger base (although in practice formed as a single unitary body)which avoids the need for double-curved surfaces as in the embodiment ofFIG. 11. This constitutes a certain simplification since the conicalsurfaces 27 a, 27 b of the two cones 15 a, 15 b can be formed asgeneratrices of straight lines. The planets 15 are carried by rollerbearings 16, 17 housed in radially elongate slots 18 in the planetcarrier 14.

The sun members 23 a, 23 b can then be formed as two disks havinginclined surfaces 26 a, 26 b although, in order to retain relativelysmall contact patches these surfaces will nevertheless be curvedsurfaces formed as surfaces of revolution of an arcuate line. The trackmembers 28 a, 28 b may likewise be formed as two disks with curvedsurfaces 29 a, 29 b with which the conical surfaces 27 a, 27 b of thetwo cone parts 15 a, 15 b of the planet 15 are in rolling contact.

For simplicity of explanation only the minimum of moving parts have beenillustrated in FIG. 12. The general concept of the mechanism issubstantially the same as previously described, with the transmissionratio being determined by the separation between the two tracks parts 28a, 28 b controlled by a suitable mechanism (not shown).

Referring now to FIGS. 13-17 the device shown comprises a bi-directionalcontinuously variable transmission device for transmitting rotary drivefrom an input shaft 211 to an output drive member 212 illustrated as atubular component to which, of course, an output drive shaft may becoupled by any known means.

The drive transmission device comprises inner and outer races 213, 214each comprising axially spaced parts 213 a, 213 b; 214 a, 214 b betweenwhich roll planet members 215 circumferentially intercalated with rollerfollower members 216 carried on a common carrier 217 from which theoutput shaft 212 projects and which is borne on the input shaft 211 by arolling element bearing 218 and on an outer casing 219 by a rollingelement bearing 220.

The common carrier 217 has respective spindles 221 extending through andsupporting the roller followers 216. Each spindle 221 is carried at itsother end by a carrier plate 222 born on the input shaft 211 by arolling element bearing 223. At this end the drive shaft 211 is born onthe casing 219 by a rolling element bearing 224.

As can be seen in FIGS. 15 and 16, the planetary members 215 aregenerally spherical bodies divided into two axially separated parts by acircumferential annular groove or channel 225 into which the adjacentroller followers 216 engage in order to guide the planetary bodies 215to turn about a rolling axis parallel to the axis of the drive shaft211. Other than their engagement with the roller followers 216 and theraces 213, 214 the planetary members 215 are unrestrained.

Contact between the planetary members 215 and the races 213, 214 takesplace at two curved surface portions 226, 227 of the planetary bodywhich, as will be appreciated from FIGS. 15 and 16 have a radius ofcurvature which is greater than the overall radius of the generallyspherical body 215.

The radial position of the planetary body 215 is determined by the axialseparation of the radially outer race parts 213 a, 213 b which axialseparation is controlled by a screw threaded interengagement between thetwo race parts themselves, for which purpose the race part 13 a issecured to a cylindrical sleeve 228 for rotation therewith. The screwthreaded inter engagement of the two race parts is represented in FIG.13 of the drawings by the balls 229. A Bowden cable 230 (see FIG. 17) isconnected with its outer sheath engaging one of the two race members 213a, 213 b and its inner cable engaged with the other such that axialforces applied between the sheath and the inner cable can cause relativeturning motion of the race parts 213 a, 213 b. Depending on thedirection of rotation of the shaft 211, this will result in axialdisplacement of the two race parts the rotation of which is limited by astop 231 which engages in a recess 232 defined between end shoulders233, 234 and a projecting head.

As will be appreciated from a consideration of FIGS. 15 and 16, relativeapproach of the two race parts 213 a, 213 b, as shown in FIG. 15, willcause the planet member 215 to be urged radially inwardly towards theaxis of the shaft 211, and this causes a corresponding separation of theparts 214 a, 214 b of the inner race 214. The forces exerted on theplanet member 215 by the inner race 214 is generated by atorque-sensitive coupling comprising a screw threaded portion of theshaft 211 engaged in correspondingly threaded portions of the parts 214a, 214 b, each of the same hand and represented in the drawing by theinterconnection balls 235, 236.

Axial displacement of the inner race parts 214 a, 214 b is limited byabutment stops 237, 238 and a priming spring 239 urges the two raceparts 214 a, 214 b apart. Thus, depending on the direction of rotationof the shaft 211, one or other of the race parts 214 a, 214 b will belimited in its axial displacement by the respective axial abutmentshoulder 237, 238 such that the screw-turning motion imparted to theother by the rotation of the shaft 211 will compensate the forcesexerted by the choice of axial separation of the two outer race parts213 a, 213 b. As illustrated in FIG. 15, with the two parts 213 a, 213 bclosely together, the planet member 215 is urged radially inwardly suchthat the inner race parts 214 a, 214 b are urged apart so that therolling contact of the planet member between the inner and outer racesresults in a low ratio in the region of 0.14:1. When the outer raceparts 213 a, 213 b are allowed to separate by action of the cable 230reducing the tension between the inner cable and outer sheath, thetorque exerted by the shaft 211 will cause the inner race parts 214 a,214 b to move towards one another increasing the transmission ratio upto a maximum of 0.62:1 as illustrated in FIG. 16. This ratio range isincreased by the enlargement of the radius of curvature of thecontacting surfaces, 226, 227 of the planet 215 in relation to theoverall general diameter of the planet itself. The load-bearing capacityof the transmission is also increased by the presence of the channels225 in the planets which allows a greater number of planets to bearranged within a transmission casing of given size. As illustrated inFIG. 14 it will be seen that there are five planet members in the array,intercalated with five roller followers each carried on a respectivespindle 221. The effective diameter is determined by the need for thepresence of the spindles 221 to transmit forces from the rollerfollowers to the carrier. Moreover, by mounting the inner race parts 214a, 214 b on a common thread axially compressive forces can be generatedregardless of the direction of rotation of the drive shaft 211 as, ineach case, the “trailing” race part will be urged towards the other whenthis contacts its respective abutment.

Turning now to FIG. 18 there is shown a transmission device in which,although still notionally continuously variable, will act to provide anumber of preferential gear ratios at which the device will stop in theabsence of overriding forces. The general configuration of the deviceillustrated in FIG. 18 is similar to that of FIG. 13 and, therefore, thesame or corresponding components will not be described again. In thisembodiment the planet members 215 have contact surfaces 226, 227composed of a plurality of annular conical surfaces each having a lineargeneratrix to form effectively annular “facets” which thereforeeffectively define a given gear ratio when in contact with thecorresponding contact surfaces of the race parts. FIGS. 19 to 24illustrate the relative positions of the inner and outer race parts forthe six gear ratios determined by the six annular facets of the planetmembers in this embodiment.

What is claimed is:
 1. A continuously variable transmission device ofthe type having: input and output drive members radially inner and outerraces; planetary members in rolling contact with said radially inner andouter races said inner race and said outer race each comprising twoaxially spaced parts connected for rotation together and relativelyaxially movable, and control means for selectively varying the axialseparation of said two axially spaced parts of one said race and thusthe radial position of the planetary members in rolling contacttherewith, means sensitive to the torque applied between twodrive-transmitting members of the transmission, said torque sensitivemeans acting both to determine the compensating variation in theseparation of the two parts of the other race and thus the transmissionratio of the device and to vary the forces exchanged between the planetsand the races normal to the interface between them.
 2. The rollingcontact continuously variable transmission device of claim 1, whereinthe means for selectively varying the axial separation of the two partsof the radially inner or outer race include two adjustment members,helical interengagement means interconnecting said adjustment memberssuch that relative turning motion of one of said adjustment membersresults in relative axial displacement of the other.
 3. The rollingcontact continuously variable transmission device of claim 1, whereinsaid other race is the radially inner race, and wherein the two parts ofthe radially inner race are carried on a shaft which is one of a driveand a driven shaft, and wherein said torque sensitive means fordetermining the relative separation of the two parts of the radiallyinner race comprise a helical interengagement means acting to react theforces exerted by the transmission of drive forces between the radiallyinner race and the planet members.
 4. The rolling contact continuouslyvariable transmission device of claim 1, wherein the planetary membersare substantially spherical and the transmission of forces between thespherical planetary members in planetary motion and one of said driveinput and output members is effected via roller follower members.
 5. Incombination: the rolling contact continuously variable transmissiondevice of claim 1, and a fixed ratio epicyclic gear in the drive trainto one of said input drive member and said output drive member.
 6. Aninfinitely variable drive transmission device comprising thecontinuously variable transmission device of claim 1, having a furtherepicyclic transmission train having one of fixed ratio gears and rollingtraction members in the drive train from its output drive member.
 7. Thecontinuously variable drive transmission device of claim 1, wherein theplanetary members each have a circumferential annular groove, the axisof said circumferential annular groove substantially coinciding with therolling axis about which the planetary member turns as it rolls incontact with the races, said annular grooves being engaged by rollerfollower members acting to guide the planetary members to maintain theirorientation in their planetary motion.
 8. The continuously variabledrive transmission device of claim 1 wherein each planetary member has aplurality of elementary annular contact surface portions each having asubstantially constant inclination to the rolling axis of the planetarymember itself.
 9. The continuously variable drive transmission device ofclaim 1, wherein the generatrix of each planetary member includes asection comprising a plurality of substantially rectilinear elementaryportions.
 10. The rolling contact continuously variable transmissiondevice of claim 3, wherein in use said torque sensitive helicalinterengagement means reacts a direct circumferential force and an axialforce having a circumferential component and said circumferentialcomponent of said axial force is substantially equal to and opposite insign from said direct circumferential force reacted by the helicalinterengagement whereby to minimize the force required to be applied tosaid control means for selectively varying the axial separation of saidtwo axially spaced parts of said one race to maintain or change atransmission ratio of said transmission device.
 11. The continuouslyvariable drive transmission device of claim 3, wherein saidtorque-sensitive means include the two axially spaced, relativelymovable parts of the said other race, each said part being itselfaxially movable in two directional senses from a central position andengageable by limit stop means whereby to allow the transmission ofrotary drive from a rotary drive input member to a rotary output memberof the transmission device in each of two opposite senses of torquetransmission.
 12. The continuously variable drive transmission device ofclaim 2, wherein said helical interengagement means has thread flightswhich are interengaged by rolling elements.
 13. The continuouslyvariable drive transmission device of claim 11, wherein said relativelymovable race parts of the torque-sensitive means are interconnected withthe input drive member by a screw-thread engagement, said screw threadedengagement of each of said movable race parts being of the same hand,whereby rotary drive is transmitted when axial displacement of a racepart is restrained.
 14. The continuously variable drive transmissiondevice of claim 13, wherein said two relatively variable race parts ofthe torque-sensitive means are oppositely axially resiliently biased.15. The continuously variable drive transmission device of claim 13,wherein said limit stop means comprise respective abutments, saidabutments being one of on, carried by, and associated with said inputdrive member.
 16. The continuously variable drive transmission device ofclaim 14, wherein the resilient biasing of said two relatively movablerace parts is achieved by a torsion spring acting between them.
 17. Thecontinuously variable drive transmission device of claim 13, wherein thetwo race parts of said one race of the transmission device, the axialseparation of which is selectively variable, are each carried on acasing of the transmission device in such a way as to have a limitedrotational displacement in each of two opposite rotational senses. 18.The continuously variable drive transmission device of claim 17, whereinthe relative axial separation of the two race parts of said one race areachieved by a helical interengagement of at least one part of said tworace parts with a fixed member of said transmission device, said tworace parts both being relatively turnable with respect to said fixedmember.
 19. A rolling contact continuously variable transmission devicehaving: input and output drive members, radially inner and outer races,planetary members in rolling contact with said radially inner and outerraces, said inner race and said outer race each comprising two axiallyspaced parts connected for rotation together and relatively axiallymovable, and control means for selectively varying the axial separationof said two axially spaced parts of one said race and thus the radialposition of the planetary members in rolling contact therewith, meanssensitive to the torque applied between two drive-transmitting membersof the transmission, said torque sensitive means acting both todetermine the compensating variation in the separation of the two partsof the other race and thus the transmission ratio of the device and tovary the forces exchanged between the planets and the races normal tothe interface between them, wherein the means for selectively varyingthe axial separation of the two parts of said one race include twoadjustment members, helical interengagement means interconnecting saidadjustment members such that relative turning motion of one of saidadjustment members results in relative axial displacement of the other,and wherein said helical interengagement means comprises a screw threadformed on the members themselves, said one of said two adjustmentmembers being turnable through at least a limited arc of movement abouta first axis and said other of said adjustment members being restrainedagainst rotary motion at least about an axis substantially parallel tosaid first axis.
 20. A continuously variable transmission device of thetype having: input and output drive members radially inner and outerraces; planetary members in rolling contact with said radially inner andouter races said inner race and said outer race comprising two axiallyspaced parts connected for rotation together and relatively axiallymovable, and control means for selectively varying the axial separationof said two axially spaced parts of one said race and thus the radialposition of the planetary members in rolling contact therewith, meanssensitive to the torque applied between two drive-transmitting membersof the transmission, said torque sensitive means acting both todetermine the compensating variation in the separation of the two partsof the other race and thus the transmission ratio of the device and tovary the forces exchanged between the planets and the races normal tothe interface between them, wherein said torque-sensitive means includethe two axially spaced, relatively movable parts of the said other race,each said part being itself axially movable in two directional sensesfrom a central position and engageable by limit stop means whereby toallow the transmission of rotary drive from a rotary drive input memberto a rotary output member of the transmission device in each of twoopposite senses of torque transmission, wherein said relatively movablerace parts of the torque-sensitive means are interconnected with theinput drive member by a screw-thread engagement of the same hand, bywhich rotary drive is transmitted when axial displacement of a race partis restrained, wherein the thread flights of said helicalinterengagement means are interengaged by rolling elements, wherein thetwo race parts of said one race of the transmission device, the axialseparation of which is selectively variable, are each carried on acasing of the transmission device in such a way as to have a limitedrotational displacement in each of two opposite rotational senses,wherein the relative axial separation of the two race parts of said onerace are achieved by a helical interengagement of at least one part ofsaid two race parts with a fixed member of said transmission device,said two race parts both being relatively turnable with respect to saidfixed member, wherein the relative turning of the two race parts of saidone race is achieved by means of a Bowden cable acting between them. 21.A continuously variable transmission device of the type having: inputand output drive members radially inner and outer races; planetarymembers in rolling contact with said radially inner and outer races saidinner race and said outer race comprising two axially spaced partsconnected for rotation together and relatively axially movable, andcontrol means for selectively varying the axial separation of said twoaxially spaced parts of one said race and thus the radial position ofthe planetary members in rolling contact therewith, means sensitive tothe torque applied between two drive-transmitting members of thetransmission, said torque sensitive means acting both to determine thecompensating variation in the separation of the two parts of the otherrace and thus the transmission ratio of the device and to vary theforces exchanged between the planets and the races normal to theinterface between them, wherein the planetary members each have acircumferential annular groove, the axis of said circumferential annulargroove substantially coinciding with the rolling axis about which theplanetary member turns as it rolls in contact with the races, saidannular grooves being engaged by roller follower members acting to guidethe planetary members to maintain their orientation in their planetarymotion.
 22. A continuously variable transmission device of the typehaving: input and output drive members radially inner and outer races;planetary members in rolling contact with said radially inner and outerraces each said race comprising two axially spaced parts, and controlmeans for selectively varying the axial separation of said two axiallyspaced parts of one said race and thus the radial position of theplanetary members in rolling contact therewith, means sensitive to thetorque applied between two drive-transmitting members of thetransmission, said torque sensitive means acting both to determine thecompensating variation in the separation of the two parts of the otherrace and thus the transmission ratio of the device and to vary theforces exchanged between the planets and the races normal to theinterface between them, wherein each planetary member has a plurality ofelementary annular contact surface portions each having a substantiallyconstant inclination to the rolling axis of the planetary member itself.23. A continuously variable transmission device of the type having:input and output drive members radially inner and outer races; planetarymembers in rolling contact with said radially inner and outer races saidinner race and said outer race comprising two axially spaced partsconnected for rotation together and relatively axially movable, andcontrol means for selectively varying the axial separation of said twoaxially spaced parts of one said race and thus the radial position ofthe planetary members in rolling contact therewith, means sensitive tothe torque applied between two drive-transmitting members of thetransmission, said torque sensitive means acting both to determine thecompensating variation in the separation of the two parts of the otherrace and thus the transmission ratio of the device and to vary theforces exchanged between the planets and the races normal to theinterface between them, wherein the generatrix of each planetary memberincludes a section comprising a plurality of substantially rectilinearelementary portions.
 24. The continuously variable drive transmissiondrive of claim 23, wherein the races have respective contact surfacesfor rolling contact with the planetary members, each havingcorrespondingly inclined elementary annular contact surface portionssubstantially matching those of the planetary members.
 25. Acontinuously variable drive transmission device of the type having:input and output drive members, radially inner and outer races,planetary members in rolling contact with said radially inner and outerraces, said inner race and said outer race each comprising two axiallyspaced parts connected for rotation together and relatively axiallymovable, and control means for selectively varying the axial separationof said two axially spaced parts of one said race and thus the radialposition of the planetary members in rolling contact therewith, meanssensitive to the torque applied between two drive-transmitting membersof the transmission, said torque sensitive means acting both todetermine the compensating variation in the separation of the two partsof the other race and thus the transmission ratio of the device and tovary the forces exchanged between the planets and the races normal tothe interface between them, wherein the relative axial separation of thetwo race parts of said one race is achieved by a helical interengagementof at least one part of said two race parts with a fixed member of saidtransmission device, said two race parts both being relatively turnablewith respect to said fixed member, and wherein the relative turning ofthe two race parts of said one race is achieved by means of a Bowdencable acting between them.
 26. A rolling contact continuously variabletransmission device of the type having: input and output drive membersradially inner and outer races; planetary members in rolling contactwith said radially inner and outer races said inner race and said outerrace each comprising two axially spaced parts connected for rotationtogether and relatively axially movable, and control means forselectively varying the axial separation of said two axially spacedparts of one said race and thus the radial position of the planetarymembers in rolling contact therewith, means sensitive to the torqueapplied between two drive-transmitting members of the transmission, saidtorque sensitive members of the transmission, said torque sensitivemeans acting both to determine the compensating variation in theseparation of the two parts of the other race and thus the transmissionratio of the device and to vary the forces exchanged between the planetsand the races normal to the interface between them, wherein said otherrace is the radially inner race, and wherein the two parts of theradially inner race are carried on a shaft which is one of a drive and adriven shaft, and wherein said torque sensitive means for determiningthe relative separation of the two parts of the radially inner racecomprise a helical interengagement means acting to react the forcesexerted by the transmission of drive forces between the radially innerrace and the planet members; and wherein in use said torque sensitivehelical interengagement means reacts a direct circumferential force andan axial force having a circumferential component and saidcircumferential component of said axial force is substantially equal toand opposite in sign from said direct circumferential force reacted bythe helical interengagement whereby to minimize the force required to beapplied to said control means for selectively varying the axialseparation of said two axially spaced parts of said one race to maintainor change a transmission ratio of said transmission device.